Parametric integrator for condition-responsive systems

ABSTRACT

A parametric integrator adapted for use in condition-responsive systems such as intruder detection devices. The integrator is normally inactive until a transient signal, uncharacteristic of a change in the condition being monitored, is received at the system input. The integrator is then rapidly switched into system circuitry for a predetermined time interval to reduce system sensitivity and thereby avoid the possibility of false alarming in response to the transient.

United States Patent Perlman 1 July 25, 1972 [$4] PARAMETRIC INTEGRATORFOR 3,231,823 1/1966 Garfield et al. ..s2s/|27 CONDITION-RESPONSIVESYSTEMS 3.444.544 5/1969 Pearson et al. ....2so/221 3,370,284 2/1968Bagno ....340/2S8 B 1 lnvenwfl Rwhtsm, 3,167,739 l/l965 Girard et al...340/258 B [73] Assignee: Detection Systems, Inc., East Rochester,

N Y, Primary Examiner-John W. Caldwell Assislan! Examiner-Robert .I.Mooney [22] 1970 Attorney-Warren W. Kurz [21] Appl. No.: 98,353

[57] ABSTRACT [52] [1.8. 8, 328/127, A parametric integrator adaptgd foruse in condilionqcspon- 250/22l sive systems such as intruder detectiondevices. The integrator [5 l] Int. Cl. ..GOBb 13/00 is n inactive um atransiem signal. unchataccristic of Field 5 Bi 250/221? 328/ I a changein the condition being monitored, is received at the 328/ 307/233 295system input. The integrator is then rapidly switched into systemcircuitry for a predetermined time interval to reduce [56] Rdmnces Cmdsystem sensitivity and thereby avoid the possibility of false UNITEDSTATES PATENTS alarming in response to the transient.

Smith ..328/l27 A.C, SOURCE l-IS 2 Claims, 3 Drawing Figures RECTIFIERAND FlLTER VOLTAGE R EGULATOR VOLTAGE REGULATOR ALARM IACTIVATOR ALARMCHANGE SENSOR ENVELOPE DETECTOR IATENTEIIJULZS I972 SHEET 2 [IF 2TRANSIENTS IINTRUDER SWITCH ACTIVATION THRESHOLD ALARM ACTIVATION 4-THRESHOLD ALARM ACTUATING CIRCUIT DAV/D E. PERL/WAN INVENTOR BY z/Mw7AGE/VT PARAMETRIC INTEGRATOR FOR CONDITION- RESPONSIVE SYSTEMS Thepresent invention relates to condition-responsive devices such asintruder detection devices.

In my co-pending commonly assigned patent application Ser. No. 858,927,filed Sept. 18, 1969, there is disclosed a single terminal photoelectricintruder detection system which detects intrusion by detecting theincrease or decrease in received signal caused by the presense of anintruder in a beam of optical energy transmitted by the system. In thissystem, an RC integrator is used to prevent false alarming from commontransient disturbances, such as flickering lights, moderate electricalnoise disturbances, and other relatively minor disruptive inputs. Inthis system, like other known conventional systems, the RC integratorreduces the system sensitivity by a fixed amount, dependent upon thespecific time constant chosen. Because of the undesirability of falsealarms, there is a tendency to use integrators having exceptionally longtime constants so as to avoid alarm activation in response to allconceivable sources of false alarming. The problem, of course, withusing an integrator having a long time constant is that relatively weakvariations in reflected energy caused by the presence of an intruder inthe beam will go undetected. Ideally, no integration at all would bedesirable since the system would respond to fast moving and low contrasttargets much more readily. However, this sensitivity would lead to thedanger of false alarming from relatively minor optical and electricaldisturbances of the type mentioned above.

In accordance with the present invention, high sensitivity and immunityto transient disturbances are both achieved in a singlecondition-responsive device by the use of a parametric integrator. Theparametric integrator of the present invention varies the sensitivity ofthe system in accordance with the type of signal received. When thereare no disturbances, little or no integration is present and maximumsensitivity is achieved. In the presence of electrical transients,flickering lights or other disturbances, however, integration isswitched in fast enough to cancel the disturbance before its effect istransmitted to the alarm activating circuit. By providing a monostablefunction to this switch, the increased integration is kept in effect forseveral seconds following the receipt of a disturbance, therebypermitting the detection circuits to reach equilibrium before theintegration is removed. It should be recognized that adding integrationonly when required is far superior to cancelling or deactivating thesystem for a period of time following the occurrence of a disturbancesince the former merely decreases sensitivity to some degree while thelatter totally disables the device during the presence of a disturbanceand for several seconds thereafter.

It is the primary object of the present invention to provide an improvedintruder detection device of high sensitivity and reliability.

Another object of the present invention is to provide a detection systemwhich iscapable of distinguishing minor signal variations produced bythe presence of an intruder from minor signal variations caused by theoccurrence of unrelated transient events and for preventing the latterfrom producing false alarms.

Still another object of the invention is to provide a parametricintegrating circuit which is adapted for use in all conditionresponsivesystems.

These and other objects of the invention will become immediatelyapparent to those skilled in the art from the ensuing detaileddescription of a preferred embodiment, reference being-made to theaccompanying drawings in which:

FIG. 1 is a block diagram and partial electrical schematic of adetection system incorporating a preferred embodiment of the invention.

FIG. 2 is a series of waveforms illustrating the outputs of varioussystem components as a function of time; and

FIG. 3 is an electrical schematic of a parametric integrator accordingto a preferred embodiment.

Referring now to FIG. I, a single terminal photoelectric detectionsystem 1 for detecting the presence of an intruder 2 in a space undersurveillance by such system is shown embodying the invention. The systemcomprises a housing 3 having disposed therein a transmitter 4 ofelectromagnetic radiation, a transducer 5 which is sensitive to theradiation provided by transmitter 4 and capable of producing anelectrical signal having an amplitude proportional to the intensity ofsuch radiation incident upon the sensitive surface thereof, andcircuitry for activating an alarm in response to predetermined rate ofchange in energy incident upon the transducer 5.

Preferably, the transmitter comprises a luminous or lightemitting diode7 (e.g., the gallium-arsenide or silicon carbide types) and a lens 8which serves to direct energy from the source outwardly from the housing3 through a space wherein intrusion is to be detected. Luminous diodesare ideal for use in such systems because of their relatively small sizeand ability to be modulated at electronic speeds. Gallium arsenideluminous diodes are particularly preferable because of their ability toemit infrared radiation which is, of course, undetectable by theintruder; therefore, he would be unable to determine the direction inwhich the system is directed even if he were aware of its presence.Luminous diode 7 is energized and sine wave modulated at a frequencywhereby room lighting and other background noise may be discriminatedagainst. Diode energization and modulation is accomplished byconventional circuitry comprising a multivibrator oscillator 9, acurrent regulator 10, and a power amplifier ll which are connected inseries with the cathode 12 of the luminous diode. Regulated voltage isprovided to the diode energizing and modulating circuit and on to theanode 13 of the luminous diode by a voltage regulator 14 which receivesthe direct current output of the rectifyting and filtering circuit 15which, in turn, is connected with a conventional alternating currentsource 16.

Transducer 5 preferably comprises a silicon photodiode which is arrangedin the housing 3 in such a manner as to receive radiant energy which hasbeen transmitted by transmitter 4 and reflected by objects in the spaceunder surveillance. A lens 20 serves to provide optical gain bycondensing reflected energy upon the radiation sensitive surface of thetransducer. The output of the transducer is then amplified bypreamplifier 2i and the output'thereof is then passed through a sharplytuned amplifier 22 which is tuned to the frequency of modulationprovided by oscillator 9. The output of tuned amplifier 22 is fed to aconventional clamping circuit 30, commonly referred to as a d.c.restorer whereby the sine wave output of the tuned amplifier may beclamped to zero volts so that the full peak-to-peak amplitude can bedetected. Because of the normal distortion associated with clampingcircuits, the lower portion of the sine wave input is clipped off byclamping circuit 30 and its output will be as shown in FIG. 2(a).Variations in the AC output of clamping circuit 30 are detected by alevel change sensor 32 which is provided with regulated voltage fromvoltage regulator 27 and is provided with a negative reference voltagefrom oscillator 9 through the rectifying and filtering circuit 28, thenegative voltage serving to enhance the output of level change sensor 32when the input decreases from a pre-existing low value. The output oflevel change sensor 32 would normally be at a constant dc. voltage whenthe input thereto is at a steady state value. When the input to sensor32 varies, however, a positive-going d.c. signal will appear on itsoutput until the input signal stabilizes at a new steady state value.This d.c. signal is proportional to the magnitude of variation in itsinput. Circuitry for this sensor is disclosed in my aforementionedco-pending application.

If an object moves into the beam and its reflectivity is less than thatof background, a decrease in the input to sensor 32 will occur.Conversely, if an object whose reflectivity exceeds that of backgroundenters the beam, the input to sensor 32 will increase. Assuming that thechange in input is greater than the detecting threshold of the sensor32, an output signal would be transmitted to the alarm activator 31.Before being fed to the alarm activator, however, the output signal ofsensor 32 is integrated by a RC integrator 33 having a relatively fastresponse time. Integrator 33 merely serves to desensitize the system tohigh frequency disturbances due to random noise which is always present.This integration, however, is not sufficient to prevent alarms due toflickering fluorescent lights and other optical and electricaldisturbances. To desensitize the system to such disturbances, aparametric integrator 34 is incorporated as shown. Parametric integrator34 comprises envelope detector 35, high pass filter 36, monostableswitch 37 and a supplemental integrating circuit 38.

The operation of the parametric integrator 34 may be best understood byreferring to FIG. 2 wherein the outputs of the various elementscomprising the parametric integrator are shown as a function of time. Asingle pulsed disturbance typical of a fluorescent light flicker isshown in the right hand portion of the waveform in FIG. 2(a), This istypical of an optical transient and may be found to occur singly, asshown, or in sustained bursts. The latter type of disturbance ischaracteristic of shot noise due to very high illumination levels andelectrical disturbances arising from nearby machinery such as motorswith arching brushes. In order for the circuit to work properly, theaverage peak value of the modulated signal is obtained in an envelopedetector having a frequency response fast enough to preserve transientswhich must be suppressed. The high pass filter blocks all signal changescharacteristic of targets or intruders and passes only fast disturbanceswhich are usually at least an order of magnitude shorter in durationthan the signal produced by fast moving intruders through the beam. Theoutput of the envelope detector and the high pass filter are shown aswaveforms (b) and (c), respectively, in FIG. 2. The output of the highpass filter activates a regenerative monostable switch which turns onvery rapidly and then remains on for several seconds following theremoval of the disturbance. This switch connects the supplementalintegrator 38 into the signal processing circuit. Since the capacitiveelement of the supplemental integrator 38 is considerably larger thanthat of integrator 33 and is initially uncharged, it acts as an initialshort circuit across the output of integrator 33, instantly removingcharge which has begun to build up across the capacitive element ofintegrator 33 in response to the transient. Response time of theintegrator switching must be fast enough so that the capacitive elementof integrator 33 is dumped before its voltage can rise to the alarmactivating threshhold value required to trigger alarm activator 31.

In FIG. 2(e) the input to the alarm activator is shown. Notice that asthe output of clamping circuit 30 varies relatively slowly, suchvariation being attributable to the presence of an intruder, theparametric integrator has no effect on the input to alarm activator 31,the input being effected solely by integrator 33. Integrator 33 willcontinue to receive a signal from sensor 32 until the sensor input hasstabilized. Thus, the alarm activator input or the output of integrator33 will appear as shown in the left portion of the waveform in FIG.2(e). Upon the occurrence of a high intensity transient, as shown in theright portion of the waveforms in FIG. 2, the output of integrator 33will increase in accordance with its time constant, until the parametricintegrator is triggered and dumps the accumulated charge on thecapacitive element of integrator 33 following which the signal at (e)will increase much more slowly in accordance with the greatly increasedtime constant associated with supplemental integrator 38.

Circuitry for the parametric integrator is illustrated in FIG. 3.Integrator 33 is comprised of the resistor R33 and capacitor C22. Theenvelope detector comprises resistor R63 and R64, diode D12, andcapacitor C26. The tie constants of the circuit are chosen so as tofilter out the modulated signal (2-2.5 KHZ in the present embodiment)while maintaining adequate speed of response to respond to the transientdisturbances which must be sensed in order for the parametric integratorto function properly. Coupling capacitor C27 serves as the high passfilter to block signal changes of the type resulting from intrusion. Theheart of the monostable switch is a programmable unijunction transistorQ18 which is a three terminal semiconductor device which switchesrapidly from a non-conducting to a conducting state when its gate leadbecomes approximately 0.6 of a volt negative with respect to its anodelead. Once switched on, the unijunction transistor will remain inconduc-. tion as long as the current flowing through it exceeds athreshhold value called the holding current and its conduction, onceinitiated, will continue after the withdrawal of turn-on voltage betweenanode and gate. In the circuitry shown, the programmable unijunctiontransistor is non-conducting because its anode and gate leads are bothconnected to the positive supply via R65 and R66, respectively.Therefore, since there is no current flow through transistor Q18, thecathode voltage at point (d) is at minus 10 volts, keeping switchingtransistor Q25 in the off condition. Diode D14 prevents excessivenegative voltage from appearing across the base-emitter junction oftransistor Q25. In this condition, capacitor C16, comprisingsupplemental integrator 38, is essentially removed from the circuit.

Upon receipt of a suitably fast transient, both a positive and negativespike will appear at the anode (c) of transistor Q18. Whereas thenegative portion of this transient has no effect, the positive portion,if it exceeds 0.6 volt, causes transistor 018 to switch on. CapacitorC28 charges rapidly via resistor R65 and the conducting programmableunijunction transistor from an initial small negative voltage to plus 13volts. Resistor R65 serves to limit this charging current to a safevalue. Diode D13 steers the positive trigger pulses from anode to gaterather than to positive supply via R65. It is important that resistorsR67 and R68 be large enough so that it is impossible for the steadystate current through transistor Q18 to reach the holding current level.Therefore, as soon as capacitor C28 approaches full charge, theprogrammable unijunction transistor ceases conduction until retriggeredby a succeeding transient. Qnce released, capacitor C28 dischargesthrough resistor R68 and the base emitter junction of transistor Q25. Solong as this discharge is sufficiently high, transistor Q25 will remainsaturated, effectively switching capacitor C16 in parallel withcapacitor C22, thereby increasing the integrator time constant andsuppressing the circuits response to the disruptive transient. ResistorR69 provides a discharge path for capacitor C16 after transistor Q25ceases conduction.

The parametric integrator described herein is capable of suppressing aconsiderable amount of severe signal fluctuations, this amount beingdetermined primarily by the value of capacitor C16 and the average valueof the disturbance. It should be clear, that even if C16 is made verylarge, a sustained disturbance having a sufficiently high average valuewill eventually cause an alarm condition to exist. The existance of sucha disturbance, however, is highly improbable so long as the device isnot exposed to very high illumination levels as might be obtained inpointing it directly at a light bulb. Further protection against falsealarms is provided by the intense transient cancelling circuit describedin my copending application Ser. No. 98,355 filed Dec. 15, 1970, andentitled Photoelectric Intruder Detection device," which totallydisables the signal processing circuit when excessively large and/orhigh speed disruptive transients occur. Since the threshhold of theintense transient cancelling circuit is set quite high compared to thatof the parametric integrator, it should be considered as a secondary oremergency defense against transients of the most severe character thatone would anticipate in any normal installation.

While the present invention has been described with particular referenceto a single terminal photoelectric intruder detection circuit, it shouldbe quite apparent that the parametric integrator has utility in anycondition-responsive system in which integration is desirable. Whileonly one embodiment of the invention has been here disclosed, it shouldbe apparent that the apparatus and particularly the particular circuitelements comprising such apparatus may all be varied widely withoutdeparting from the spirit and scope of the invention as defined in theappended claims.

Iclaim:

l. A parametric integrator for suppressing the effect of transientoccurrences in a condition-responsive circuit, said integratorcomprising in series a high pass filter adapted to pass signals having asubstantially higher frequency than the frequency of the condition to besensed, a normally nonconductive monostable switch adapted to switch toa conducting state for a predetermined time in response to the passageof a signal by said filter, and an RC integrator adapted to be connectedto said circuit when said switch is in a conducting state.

2. For use in a photoelectric intruder detection device comprisingtransmitting means for directing a beam of electromagnetic radiationinto a space wherein the intrusion is to be sensed, transducing meanspositioned to receive radiation from said transmitting means as modifiedor reflected by objects in said beam for providing an electrical outputsignal having an amplitude proportional to the intensity of receivedradiation, signal level sensing means operably coupled with saidtransducing means output for providing a signal whenever saidtransducing means output varies with a magnitude and at a rate in excessof a predetermined value, first integrating means, operably coupled withsaid signal level sensing means output for integrating said sensingmeans output, and means for activating an alarm whenever the integratedsignal exceeds a predetermined threshhold value, the improvementcomprising a second integrating means having a time constantsubstantially longer than said first integrating means and beingnormally disassociated with said device, and means for connecting saidsecond integrating means in parallel with said first integrating meansfor a predetermined period following a transient signal on the output ofsaid sensing means, said transient signal having a frequencysubstantially greater than that normally encountered by the passage ofan intruder through said beam.

* 1|K t I.

1. A parametric integrator for suppressing the effect of transientoccurrences in a condition-responsive circuit, said integratorcomprising in series a high pass filter adapted to pass signals having asubstantially higher frequency than the frequency of the condition to besensed, a normally nonconductive monostable switch adapted to switch toa conducting state for a predetermined time in response to the passageof a signal by said filter, and an RC integrator adapted to be connectedto said circuit when said switch is in a conducting state.
 2. For use ina photoelectric intruder detection device comprising transmitting meansfor directing a beam of electromagnetic radiation into a space whereinthe intrusion is to be sensed, transducing means positioned to receiveradiation from said transmitting means as modified or reflected byobjects in said beam for providing an electrical output signal having anamplitude proportional to the intensity of received radiation, signallevel sensing means operably coupled with said transducing means outputfor providing a signal whenever said transducing means output varieswith a magnitude and at a rate in excess of a predetermined value, firstintegrating means, operably coupled with said signal level sensing meansoutput for integrating said sensing means output, and means foractivating an alarm whenever the integrated signal exceeds apredetermined threshhold value, the improvement comprising a secondintegrating meAns having a time constant substantially longer than saidfirst integrating means and being normally disassociated with saiddevice, and means for connecting said second integrating means inparallel with said first integrating means for a predetermined periodfollowing a transient signal on the output of said sensing means, saidtransient signal having a frequency substantially greater than thatnormally encountered by the passage of an intruder through said beam.